Cetane improver for diesel fuel oils



United States Patent 3,380,815 CETANE IMPROVER FOR DIESEL FUEL OILS Walter Alexander Herbst, Union, NJ., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed May 4, 1965, Ser. No. 453,215

6 Claims. (Cl. 44-57) The present invention relates to diesel fuel oils. In general, it concerns a diesel fuel oil of improved ignition qauilty. In particular it relates to diesel fuel oils having incorporated therein a small amount of a gem dinitroalkanoate as a cetane improver.

One of the most important properties of a diesel fuel oil is ignition quality, i.e. its ability to burn spontaneously under the pressure and temperature conditions which exist in the engine cylinder. In general, it has been shown that case of starting, knocking or detonation, and, to a certain extent, excessive smoke and engine oarbonization are caused or accentuated by fuels of poor ignition quality.

Cetane number is an index of a diesel fuel oils ignition quality. It is measured in a single cylinder, variable compression ratio diesel engine under fixed conditions of speed, load, jacket temperature, inlet air temperature, etc. The ignition quality of the test fuel oil is compared with mixtures of two reference hydrocarbon fuels, name ly, cetane, which is assigned the rating of 100 and alphamethyi-naphthalene which is assigned the rating 0. In general, the more parafiinic a fuel is the better will be its ignition quality. Aromatic fuels are relatively poor in this respect. Cetane accordingly represents a parafiinic fuel of excellent ignition quality, while alpha-methylnaphthalene typifies an aromatic fuel of very poor ignition quality. Cetane number is the percent of pure cetane in a blend of cetane and alpha-methyl-naphthalene which matches the ignition quality of the fuel sample being tested. For example, if the mixture of 47% cetane and 53% alpha-methyl-napthalene shows the same ignition quality in the test engine as the test fuel, then the test fuel is said to have a cetane number of 47. Cetane numbers in the present invention were determined according to the cetane method (ASTM D463).

As in practically all petroleum products, additives are finding increasingly wide application in diesel fuel oils. Cetane improvers are additives which are effective in improving ignition quality of diesel fuel oils. Amyl nitrate is one of the better known cetane improvers. It is capable of raising the cetane number of 40 cetane fuel to about 45 at a cost of approximately per gallon of fuel oil. Cetane improvers, for example, amyl nitrate, are usually employed at about 1 wt. percent concentration. Heretofore, cetane improvers have not been used widely in diesel fuel oils primarily because their cost has not been competitive with crude selection and refinery finishing.

According to the present invention, it has been discovered that gem dinitroalkanoates, e.g. methyl 4,4-dinitropentanoate, unexpectedly increase the cetane number of diesel fuel oils and, moreover, do so at relatively low concentrations.

Diesel fuel oils as referred to in connection with the present invention consist of at least 95% of a mixture of hydrocarbons boiling between 250 F. and 750 F. as determined by either ASTM method D-86-59 when their end points do not exceed 600 F. or by ASTM method D15859. Diesel fuel oils are defined by ASTM specification D97553T (and later versions of the same specification) and fall into grades 1D, 2D and 4D. The diesel Patented Apr. 30, 1968 ice fuel oils have viscosities between 1.4 and 26.4 centistokes at F. The cetane improver of the present invention may be employed in any of these diesel fuel oils.

The cetane improver employed in the diesel fuel oils of the present invention is a gem dinitroalkanoate. Suitable gem dinitroalkanoates can be represented by the formula:

wherein R is selected from the group consisting of hydrogen and C to C alkyl groups, R is a straight chain alkyl group containing 1 to 5 carbon atoms, and R is an alkyl group containing 1 to 3 carbon atoms. Illustrative examples of such gem dinitroalkanoates include, but are not limited to, ethyl 3,3-dinitropropanoate, propyl 2,2dinitrobutanoate, methyl 4,4-dinitroheptanoate, ethyl 5,5-dinitrohexanoate, and the like. Methyl 4,4-dinitropentanoate is preferred.

The preparation of gem dinitroalkanoates is known in the art. One such preparation involves the base-catalyzed condensation of a dinitroalkane and an u-fl unsaturated ester. For example, methyl 4,4-dinitropentanoate may be prepared by condensing (in an aqueous potassium hydroxide media) l,l-dinitroethan and methyl acrylate.

The cetane improver of the present invention will be employed in the diesel fuel oil at various concentrations depending, for example, upon the particular diesel fuel oil employed, the desired cetane number, etc. In general, while about 0.04 to 4 wt. percent of the cetane improver can be used, preferably about 0.1 to 2 wt. percent is employed. A most preferred composition of the present invention contains about 0.5 wt. percent methyl 4,4-dinitropentanoate.

In order to demonstrate the utility and the efiicacy of the compositions of the present invention, the following examples are included.

EXAMPLE 1 A base fuel oil and a base fuel oil +0.44 wt. percent methyl 4,4-dinitropentanoate were tested in a cetane rating engine according to cetane method (ASTM D-163). The base fuel Oil was a Number 2 diesel fuel oil having the following typical inspections:

The methyl 4,4-dinitropentanoate was obtained from the Hummel Chemical Co., New York. Table I shows the results of the tests in the cetane rating engine.

Table I Cetane number Base fuel oil 37.3 Base fuel oil +0.44 wt. percent methyl 4,4-dinitropentanoate 56.9

The results in Table I show an improvement in cetane number of almost 20 points by incorporating a small amount of methyl 4,4-dinitropentanoate into the diesel fuel oil.

In order to demonstrate the effect of various compounds on the cetane number of a diesel fuel oil the data shown in Table II were obtained. This data show that methyl 4,4-dinitropentanoate, one of the gem dinitroalkanoate cetane improvers of the present invention, is much more effective, i.e. about 16 points, than the other nitro compounds compared e.g. 2-nitropropanol, 2-nitroethanol and butylnitroamine.

Table II Cetane number Additive (0.44 wt. percent): of blend Base fuel oil 1 37.3 2 nitropropanol 40.1 2 nitroethanol 39.8 Butylni'troamine 40.5 Methyl 4,4-dinitropentanoate 56.9

1 As described in Example 1.

It was further discovered that gem dinitroalkanoates are more effective than amyl nitrate, the major active component in a commercially available cetane improver, i.e. Ethyl Diesel Ignition Improver. For example, n-am-yl nitrate in a 40 cetane number diesel fuel oil similar to the one used above affects the cetane number as shown in Table III.

Table III Cetane number Wt. percent amyl nitrate increase The data in Table III show that about 2 wt. percent n-amyl nitrate would give a cetane number increase equal to that obtained by the use of about 0.5 (e.g. 0.44) wt. percent of a gem ditnitroalkanoate of the present invention.

In addition to the cetane improver, diesel fuel oil compositions of the present invention may contain other additives commonly used in diesel fuel oils. For example, stabilizers against gum and sediment formation in storage, emulsion breakers, rust inhibitors, pour point depressants and the like may be employed in the compositions. Many comercially available diesel fuel oils will contain such additives.

EXAMPLE 2 A diesel fuel oil of improved ignition quality containing a cetane improver of the present invention and other additives may consist of No. 1-D diesel fuel oil to which is added about 0.5 wt. percent of ethyl 3,3-dinitropropanoate, 0.008 wt. percent of an inhibitor such as Primene 81R (an alkylamine) 0.0025 wt. percent of an ashless dispersant (e.g. a terpolymer of alkyl fumarate, vinyl acetate and C oxochloro propylene oxymaleate) and 0.001 wt. percent of a demulsifier such as Aliquot 221 4 (a quaternary ammonium compound). Typical properties of such a fuel oil are as follows:

In other instances about 0.003 wt. percent of an antirust agent (e.g. Santolene C) and/or 0.0003 wt. percent of a metal deactivator (e.g. Du Pont metal deactivator) may also be present.

Many modifications of the above-described examples can be made without departing from the spirit and scope of the invention.

What is claimed is:

1. A diesel fuel oil composition of improved ignition quality comprising a major amount of a diesel fuel oil and a minor amount sufficient to increase the cetane number of said diesel fuel oil of a gem dinitroalkanoate.

2. A composition as defined by claim 1 wherein said gem dinitroalkanoate has the formula:

wherein R is selected from the group consisting of hydrogen and C to C alkyl groups, R is a straight chain alkyl group containing 1 to 5 carbon atoms and R is an alkyl group containing 1 to 3 carbon atoms.

3. A composition as defined by claim 2 wherein said minor amount is about 0.04 to about 4 wt. percent.

4. A diesel fuel oil composition of improved ignition quality comprising a major amount of diesel fuel oil and about 0.04 to 4 wt. percent methyl 4,4-dinitropentanoate.

5. A diesel fuel oil composition of improved ignition quality comprising a major amount of a diesel fuel oil and about 0.5 wt. percent methyl 4,4-dinitropentanoate.

6. A diesel fuel oil composition of improved ignition quality comprising a major amount of a diesel fuel oil and about 1.0 wt. percent ethyl 3,3-dinitropropanoate.

References Cited UNITED STATES PATENTS 2,380,341 7/ 1945 Sowers 4457 2,387,403 10/1945 McCracken et al. 4457 2,387,279 10/1945 McCracken 4457 2,560,904 7/ 1951 Sugimoto 44-57 DANIEL E. WYMAN, Primary Examiner.

Y. H. SMITH, Assistant Examiner. 

1. A DIESEL FUEL OIL COMPOSITION OF IMPROVED IGNITION QUALITY COMPRISING A MAJOR AMOUNT OF A DIESEL FUEL OIL AND A MINOR AMOUNT SUFFICIENT TO INCREASE THE CETANE NUMBER OF SAID DIESEL FUEL OIL OF A GEM DINITROALKANOATE. 